System and Method for Identifying the Path or Devices on the Path of a Communication Signal

ABSTRACT

A system and method of applying a known modification in the form of a distortion to a signal to enable a determination if a signal received by a first node is received directly from a second node or indirectly through a repeater. The repeater receives a primary signal and creates a secondary signal as a function of the primary signal and a known distortion, wherein the known distortion identifies the repeater. The primary signal is transmitted and injected with the secondary signal as the first signal to the primary receiver.

CROSS REFERENCES

The present application is a continuation of and claims priority benefitto co-pending U.S. application Ser. No. 12/908,627 titled “SYSTEM ANDMETHOD FOR IDENTIFYING THE PATH OR DEVICES ON THE PATH OF ACOMMUNICATION SIGNAL”, filed 20 Oct. 2010; which is a continuation ofU.S. application Ser. No. 10/586,745 titled “SYSTEM AND METHOD FORIDENTIFYING THE PATH OR DEVICES ON THE PATH OF A COMMUNICATION SIGNAL”,filed 23 Jun. 2008; which is a national stage application of PCTApplication No. PCT/US2005/016453 titled “SYSTEM AND METHOD FORIDENTIFYING THE PATH OR DEVICES ON THE PATH OF A COMMUNICATION SIGNAL”,filed on 11 May 2005; which claims priority to each of the followingU.S. provisional patent applications: Provisional Application Ser. No.60/570,082, titled “SYSTEM AND METHOD FOR IDENTIFYING THE PATH ORDEVICES ON THE PATH OF A COMMUNICATION SIGNAL”, filed 12 May 2004;Provisional Application Ser. No. 60/570,081, titled “SYSTEM AND METHODFOR IDENTIFYING THE PATH OR DEVICE ON THE PATH OF A COMMUNICATION SIGNALUSING (1+r(t)) AMPLITUDE MODULATION”, filed 12 May 2004; and ProvisionalApplication Ser. No. 60/570,067, titled “SYSTEM AND METHOD FOR DETECTINGA MOBILE STATION OPERATING THROUGH A REPEATER”, filed 12 May 2004; theentirety of each of the foregoing is hereby incorporated herein byreference.

BACKGROUND

Applicant's disclosure is directed generally towards a wirelesscommunications network for determining whether a signal from a mobileappliance is operated on by a repeater or other network device.

The use of wireless communication devices such as telephones, pagers,personal digital assistants, laptop computers, etc., hereinafterreferred to collectively as “mobile appliances,” has become prevalent intoday's society.

FIG. 1 shows a conventional mobile-appliance communication system havingbase stations 10 a-c for communicating with a mobile appliance 20. Eachbase station 10 contains signal processing equipment and an antenna fortransmitting to and receiving signals from the mobile appliance 20 aswell as other base stations. A Base Station Controller (“BSC”) and/orMobile Switching Center (“MSC”) 45 typically is connected to each basestation 10 through a wire line connection 41.

To meet the ever growing demand for mobile communication, wirelesscommunication systems deploy repeater stations to expand range andconcentration of coverage. In FIG. 1, a repeater 50 a, associated withbase station 10 a, is located to extend the coverage area to encompassthe back side of the mountain 1. The repeater 50 b, associated with basestation 10 c, is mounted on a building and is used to provide servicewithin the building 2.

Repeaters typically fall into two categories: (1) non-translating, alsoknown as wideband, and (2) translating, also known as narrowband. Asshown in FIG. 2 a, a non-translating repeater 250 simply passes theforward F_(f1) and reverse R_(f1) frequencies from the base station 210and mobile appliance 220 respectively to and from the repeater coveragelocation. Often wideband repeaters are “in-building” or serve limitedcoverage areas. While the description of non-translating repeaters aboveand translating repeaters below are described in reference to frequency,their operation can equally be described in terms of channels, and theuse of the term frequency should not be construed to limit the scope ofthe present disclosed subject matter.

A translating repeater assigns the mobile to a different traffic channelunbeknownst to the base station, mobile switch, MSC, and the basestation controller. As shown in FIG. 2 b, the translating repeater usesthe base station traffic channel R_(f1) for repeater 250 to base station210 communication while the mobile appliance 220 utilizes a separatefrequency R_(f2) for mobile to repeater communications. Translatingrepeaters act similarly in the forward direction using F_(f1) from thebase station 210 to the repeater station 250 and F_(f2), from therepeater station 250 to the mobile appliance 220. In both cases, theexistence of the repeater is usually transparent to the network.

The function of the repeater station can be assumed to be equivalent toconverting all signals in some received bandwidth from a Radio Frequency(RF) to some Intermediate Frequency (IF). The IF signal bandwidth isthen up-converted by suitably frequency shifting this bandwidth whileconcurrently applying both amplification and a fixed delay to thesignals.

For example, let the set of signals transmitted by N mobiles in therepeaters' input bandwidth be denoted by

${{S(t)} = {\sum\limits_{k = 1}^{N}{{a(k)}{x\left( {k,t} \right)}{\sin ({wt})}}}},$

where the signal from a given mobile is denoted by x(k, t). The signalx(k, t) is contained in the repeater bandwidth and w is the angularfrequency center of the RF bandwidth. The repeater downshifts theaggregate signal to generate

${{D(t)} = {\sum\limits_{k = 1}^{N}{{a(k)}{x\left( {k,t} \right)}{\sin ({vt})}}}},$

in which v is now representative of the center of the IF bandwidth. Theentire signal D(t) is now converted back to RF by operations that areequivalent to forming the signal

${{R\left( {t + T} \right)} = {{G{\sum\limits_{k = 1}^{N}{{a(k)}{x\left( {k,t} \right)}{\sin ({vt})}{\cos \left( {{wt} - {vt}} \right)}}}} + {G{\sum\limits_{k = 1}^{N}{{a(k)}{x\left( {k,t} \right)}{\cos ({vt})}{\sin \left( {{wt} - {vt}} \right)}}}}}},$

in which G is the repeater gain. The last equation can be written in amore convenient, mathematical manner by noting that R(t) can be derivedfrom D(t) by writing it as R(t+T)=Re{G exp(j(w−v)tI(t))}, where Gexp(j(w−v)t) is the complex representation of the multiplicative signalintroduced by the repeater on the downshifted signal bandwidth and I(t)is the complex representation of D(t).

Essentially, the function of the repeater is to convert the RF signal toan IF signal, delay and amplify that IF signal, up-convert the signalback to RF, and transmit the signal. This is true for both translatingand non-translating repeaters.

Repeaters typically communicate with the host base station via an RFlink as shown in FIG. 3 between base station 310 and repeater 350 a.This connection allows remote operation of the repeater without physicalties back to the host base station, which is particularly advantageousin rugged or other areas where laying lines is difficult or costly. Somerepeaters, generally non-translating repeaters, use a fiber optic orcopper wire “tether” instead of an RF link to communicate with the hostbase station as shown in FIG. 3, where base station 310 is connected torepeater station 350 b by tether 351. RF signals are placed onto thetether at the repeater and then summed into the normal base stationantenna path at the antenna feed interface 311 at the host base station.After integration into the normal base station antenna path, the signalfrom the repeater is indistinguishable to the base station regarding itsorigin (e.g., from the base station antennas or from a tether). In thistether architecture as well, the host base station has no knowledge ofthe repeater's existence or that a call is being served by the repeater.

Neither the base station nor the switch knows that a repeater or othernetwork device is serving a call. For example, a repeater installed asan in-building distribution system would use indoor antennas tocommunicate with the indoor handsets and an outdoor antenna tocommunicate with the host base station. In order to accomplish this,there is a need to overcome the deficiencies in the prior art byemploying a novel system and method that is capable of identifying whena mobile's signal is being received via a repeater or other networkdevice.

In view of this need, it is an object of the disclosed subject matter topresent a method for determining whether a signal is received directlyfrom the mobile or from a repeater in the communication network.

These objects and other advantages of the disclosed subject matter willbe readily apparent to one skilled in the art to which the disclosurepertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art wireless communication system.

FIG. 2 a is an illustration of the operation of a prior artnon-translating repeater station.

FIG. 2 b is an illustration of the operation of a prior art translatingrepeater station.

FIG. 3 is an illustration of a prior art wireless communication systemwith repeater stations connected with an RF link and over a tether.

FIG. 4 is a schematic of an embodiment of a communication systemaccording to an embodiment of the present subject matter.

FIG. 5 is a flowchart of a method for determining if and, if so whichnetwork device has operated on a signal according to an embodiment ofthe present subject matter.

DETAILED DESCRIPTION

An important aspect of the presently disclosed subject matter is that anetwork analysis system can determine when a received signal from amobile has passed through a repeater. Prior art systems do not have thiscapability and consequently treat all the signals received by the basestation as having been received directly from the target mobile. Forexample, the ability to determine if a signal from a mobile has passedthrough a repeater enables embodiments of the disclosed subject matterin a network analysis system to provide more efficient networkmanagement. The foregoing embodiments are exemplary only and shall notbe used to limit the invention.

The present subject matter relates to the case where signals can bereceived at base stations, or other receivers, either directly from themobile appliance or through a repeater. The ability to discern thedifference between direct signals and repeated signals (i.e., signalsthat arrive via a repeater) allows the network analysis system tocollect data important to system operators. In the forthcomingdiscussions the subject matter will be described in terms of a networkanalysis system, however as noted above, any network receiver or sensorreceiving a signal from the repeaters can employ the described method.

This disclosed subject matter allows repeater identification via theinsertion of a distortion encoded onto, over or into the primary signalin such manner that it is transparent to the primary receiver, such as abase station, mobile station or other network device such that theoperation of the primary receiver remains identical in the presence orabsence of the secondary information obtainable attributable to thedistortion. The secondary information attributable to the distortion,however, because of its transparency is only recoverable by a secondaryreceiver which has access to both the input and output of the primaryreceiver. However, implementation of the present subject matter mayinclude a primary receiver and secondary receiver sharing somecommonality, and need not actually be physically separated. Thesecondary information is inserted as a secondary signal or secondarysignals at one or more devices in the path of the primary signal as ittraverses from the transmitter to the primary receiver

An aspect of the current subject matter involves the formation of thesecondary signal. The secondary signal is formed as a function of boththe device through which the primary signal passes and the primarysignal. Mathematically, s′(t) represents the secondary signal injectedat a device with distortion i, s′(t)=f(i,s(t)). The function f( )represents the mapping and s(t) of course the primary signal.

The secondary signal is modified such that it appears to be a componentof the distortion of whatever nature, experienced on the channel or linkof the communication signal. Distortions typically on a communicationlink or path are thermal noise or other interfering signals, howeverother introduced distortions are also envisioned. If, for example, thedistortion is additive noise, the modification is to scale the secondarysignal so that it is below the power level of the noise, thusimperceptible to the primary receiver. The Secondary signal istransmitted within the same channel as the primary signal, that is thesame time period, slot, bandwidth or other generic channelcharacterization.

An aspect of the disclosed subject matter that needs to be highlightedis that the secondary signal s′(t) is formed as a function f( ) of theprimary signal and the distortion i. As noted above, the second signaldiffers based not only on the particular repeater but also on theprimary signal that is input to the repeater. As shown in FIG. 4, therepeater 402 receives a primary signal from the mobile appliance 401 orother network transmitter. The primary signal s(t) is then operated onby a function f(s(t), i) where i is distortion unique to the repeater.The output of the repeater is a signal w(t), where w(t) including boththe primary signal s(t) and the secondary signal s′(t). The networkanalysis system 403 then receives and processes the signal w(t) asdescribed below to determine if the signal was received via a repeaterand, if so, the specific repeater.

The function f( ) generating the Secondary Signal from the primarysignal and the known distortion has the property that given the outputof the primary receiver, i.e. the primary signal, and the receivedsignal, the function can be inverted so that the particular distortionis revealed.

The secondary receiver may have access to both the input and the outputof the primary receiver. The secondary receiver removes the primarysignal from the input signal at the primary receiver, thus exposing thesecondary signal. That secondary signal may also receive the transmittedsignal independently of the primary receiver and only require theprimary signal from the primary receiver.

The secondary receiver implements the inverting function given byi=g(s′(t), s(t)) where g( ) inverts f( ). With the distortion i thenrevealed, the secondary receiver may then identify the device associatedwith the determined distortion i. The present subject matter equallyenvisions multiple devices in the path may be identified using theappropriate function g( ) that represent the need inversions for eachfunction f( ) each of which may have been operating at different devicelocations along the primary signal path. For example if a primary signaltransmitted from a mobile through a first repeater and then a secondrepeater and finally to a base station, the primary signal would beinjected with a distortion from the first repeater as a f₁( ) resultingin a transmitted signal w(t)=s(t)+f₁(s(t), i₁), the primary signal isthen operated on by the second repeater in which a signal is injectedwith a second distortion from the second repeater as a f₂( ) resultingin a second transmitted signal w₂(t)=w(t)+f₂(w(t), i₂). The primaryreceiver extracts the primary signal s(t) and provides it to thesecondary receiver, the secondary receiver then using g₂( ), the inverseof f₂( ), obtains the distortion associated with the second repeater i₂and then using g₁( ) the inverse of f₁( ), the distortion associatedwith the first repeater i₁ is obtained. This process may continue forany number of repeaters or network devices operating on the signalreceived by the primary receiver. f₁( ) and f₂( ), and similarly theirinverses g₁( ) and g₂( ), need not be different, only the distortions ineed be unique to the network device, if they are to be distinguished.

FIG. 5 is a flow chart for an embodiment of the current subject matter.The communication system 500 includes for illustration only, a mobile502, a repeater 509 and a primary and secondary receivers 520 and 530.The mobile unit transmits a signal s(t) which is received at therepeater 509. The repeater in addition to amplifying the signal alsocreates a secondary signal s′(t) as a function of a unique distortion iand the primary signal s(t) as shown in block 511. This secondary signalis inserted into the primary signal in block 512 and the repeatertransmits the resultant signal w(t) as shown in block 513.

The primary receiver 520 receives the repeater transmitted signal w(t)in block 521 and outputs the primary signal s(t) in block 522, the datafrom the primary signal is then extracted as shown in block 523. Theoperation of the primary receiver in the current subject matter isunaffected by the secondary signal.

The secondary receiver receives the first signal w(t) and the primarysignal s(t) from the primary receiver as shown in blocks 531 and 532respectively. With the primary signal and the first signal w(t), aninverse function g( ) of f( ) is used to determine the distortion i, ifany applied to the signal as shown in block 533. From the distortion i,the secondary receiver can determine if the received signal was operatedon by a network device and if so by comparing the distortion to knowndistortions deter mine which repeater operated upon it as shown in block534.

The co-channel secondary signal is generated by applying a specific formof Amplitude Modulation (AM) to the entire repeater signal bandwidth andserves as an identifier, identifying that a mobile or othercommunication system device is being served through a particularrepeater station, whose identity can be uniquely determined from the RFcharacteristics introduced by the repeater itself. The magnitude of theinband signal as well as any adjacent channel interference caused by theAM process can be controlled. When no signal is present in the repeaterpass-band, the AM process generates a signature signal buried deepwithin the noise. When a signal is present, the secondary signal can betransformed to uniquely identify the repeater or network device.

Thus, for example in an active cellular channel, the introduced repeateridentification signal, the secondary signal can be at a power level 9 dBor lower than the primary signal; whereas, in an inactive channel, thesecondary signal will be 9 dB or lower than the preexisting noise inthat channel. In every channel, the corresponding signature signal ispreferably at a power level 9 dB or lower than the pre-existing signallevel in that channel. The 9 dB value is chosen simply to quantify theconcept and any other number can be selected with equal applicability.For a given primary signal s(t), it is apparent that the secondarysignal s′(t) distinguishes the particular repeater. Thus each repeaterhas a unique secondary signal derived from the unique distortion i.

The collection of such distortions i over a set of repeaters, denoted S,may be drawn from sets of waveforms with specific properties, in thecase where the distortion is an interfering signal. For example, the setS may be orthogonal, quasi-orthogonal, or shift-orthogonal. Theproperties of the distortions used to generate the set S will, amongother things, depend on the number of repeaters implemented in acellular system cell or sector. Code sequences such as Golay-Hadamardand other sequences are equally envisioned when appropriate.

No constraint exists on combining the scheme of this subject matter withother schemes to identify a repeater. For example, in a GSM cellularprotocol, a parameter termed the Timing Advance (TA) parameter may beused to identify the radius at which a particular mobile may be located.This TA parameter may be used jointly with the scheme proposed here toincrease the number of identifiable repeaters in a cell or sector.

While preferred embodiments of the present inventive system and methodhave been described, it is to be understood that the embodimentsdescribed are illustrative only and that the scope of the embodiments ofthe present inventive system and method is to be defined solely by theappended claims when accorded a full range of equivalence, manyvariations and modifications naturally occurring to those of skill inthe art from a perusal hereof.

What we claim is:
 1. In a communication system including a first node, asecond node, and a repeater, wherein the first node receives a firstsignal from the second node either directly or via the repeater, amethod of applying a known distortion to a signal to enable adetermination of a signal received by the first node is receiveddirectly from the second node or indirectly through the repeater,comprising the steps of: at the repeater receiving a primary signal andcreating a secondary signal as a function of the primary signal and aknown distortion, wherein the known distortion identifies the repeater,transmitting the primary signal injected with the secondary signal asthe first signal to a primary receiver.
 2. The method of claim 1 whereinthe communication system is a wireless communication system.
 3. Themethod of claim 1 wherein the primary receiver is a network analysissystem.
 4. The method of claim 1 wherein the second node is a mobileunit.
 5. The method of claim 1, wherein the secondary signal istransmitted 9 db or less than the primary signal.
 6. A communicationsystem comprising: a first node including a transmitter for transmittinga first signal; a repeater comprising: a receiver for receiving saidfirst signal; circuitry for creating a known distortion signal andcombining said distortion signal with said received first signal tothereby form a combined signal, wherein said distortion signalidentifies said repeater; and a transmitter for transmitting saidcombined signal; a second node comprising a receiver for receiving areceived signal from either said first node or said repeater; andcircuitry for determining if said received signal is said first signalor said combined signal.
 7. The system of claim 6 wherein thecommunication system is a wireless communication system.
 8. The systemof claim 6 wherein the second node is a mobile unit.